Re: [Qemu-devel] [Qemu-trivial] [PATCH] srp: Don't use QEMU_PACKED for single elements of a structured type

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Aug 10, 2012 at 10:03:27PM +0200, Stefan Weil wrote:
> QEMU_PACKED results in a MinGW compiler warning when it is
> used for single structure elements:
> 
> warning: 'gcc_struct' attribute ignored
> 
> Using QEMU_PACKED for the whole structure avoids the compiler warning
> without changing the memory layout.

Quick link for other reviewers:
http://gcc.gnu.org/onlinedocs/gcc-4.7.1/gcc/Type-Attributes.html#Type-Attributes

> 
> Signed-off-by: Stefan Weil <sw@weilnetz.de>
> ---
>  hw/srp.h |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/srp.h b/hw/srp.h
> index 3009bd5..5e0cad5 100644
> --- a/hw/srp.h
> +++ b/hw/srp.h
> @@ -177,13 +177,13 @@ struct srp_tsk_mgmt {
>      uint8_t    reserved1[6];
>      uint64_t   tag;
>      uint8_t    reserved2[4];
> -    uint64_t   lun QEMU_PACKED;
> +    uint64_t   lun;
>      uint8_t    reserved3[2];
>      uint8_t    tsk_mgmt_func;
>      uint8_t    reserved4;
>      uint64_t   task_tag;
>      uint8_t    reserved5[8];
> -};
> +} QEMU_PACKED;

Here I actually see a difference for the uint64_t task_tag field.
Previously it was not packed, now it is packed and because it has 4 *
uint8_t before it there will be a difference in layout.

Looking at how QEMU accesses srp_tsk_mgmt, I think we're safe because we
never actually access task_tag?

Ben: Any thoughts on this patch?

Stefan